The present invention relates to a drill accessory. More particularly this invention concerns a hole saw for use with an electric drill or the like.
It is necessary when, for instance, electrical work is being done often to drill relatively large-diameter holes in plaster, plasterboard, or the like. For such an operation a twist bit is completely unusable, as it is impossible to obtain the necessary large diameter. Similarly the use of a space woodboring bit or an auger bit makes the operation relatively time consuming, and furthermore even these types of bits are unsuitable when it is necessary to drill a hole greater than 1 or 2 inches in diameter.
Such a large-diameter hole is typically formed by means of a hole saw which comprises an annular cup or crown member carried on or having a shank that is received within the chuck of the drill being used. In the bottom of the annular member or cup there is a bore centered on the axis and in which is received the shank of a pilot bit whose tip projects beyond the rim of the cup. The rim of this cup is provided with a plurality of teeth. Thus the shaft of the hole saw is fitted in the chuck of a drill and the tip of the pilot bit is placed in the center of the area where the larger-diameter hole is to be drilled. On rotation of the assembly the pilot bit will drill a predetermined distance into the material, whereupon the teeth on the rim of the cup will engage the workpiece and form therein an annular groove centered on the rotation axis of the hole saw. Thereafter the entire assembly is pushed through the workpiece until the hole saw cuts therefrom an annulus having an outer diameter equal to the desired hole diameter, minus of course twice the radial thickness of the teeth.
Such an assembly allows a relatively large-diameter hole to be drilled rapidly, as the only material removal that is necessary is that removal at the circumference of the hole and in the center at the pilot bit. Unlike spade and anger bits all of the material removed is not reduced to chips or shavings.
The considerable disadvantage of this type of arrangement is that a great deal of dust is often generated. This problem is particularly troublesome when the hole saw is being used to drill plaster or stone, as the particles produced thereby are of a highly abrasive nature so that they can do considerable damage to the mechanism of the drill should they enter this mechanism. Furthermore when the hole is being drilled in an area that has furniture or carpeting in it the user must be extremely careful to cover all of the potentially damageable furnishings in order to protect them from the dust thus generated.